Casting the Slow spell fires a projectile that slows the target enemy creature to half their normal movement speed. The creature affected will move and attack as a slower speed and will appear with a red ring around it.
"A cunning, web-like spell that reduces the target creature’s speed, giving him or her a distinct disadvantage in combat. If the creature is currently under the Haste Creature spell, Slow nullifies its effects and returns the creature to ‘normal speed’."
— Dungeon Keeper 2 Manual
A spell unique to the Vampire, casting it fires a weblike missile towards the enemy and slows their movement and attack speeds if it hits.